Skyrmion Jellyfish in Driven Chiral Magnets

Abstract

Chiral magnets can host topological particles known as skyrmions, which carry an exactly quantised topological charge $Q=-1$. In the presence of an oscillating magnetic field ${\mathbf{B}}_1(t)$, a single skyrmion embedded in a ferromagnetic background will start to move with constant velocity ${\mathbf{v}}_{\text{trans}}$. The mechanism behind this motion is similar to the one used by a jellyfish when it swims through water. We show that the skyrmion's motion is a universal phenomenon, arising in any magnetic system with translational modes. By projecting the equation of motion onto the skyrmion's translational modes and going to quadratic order in ${\mathbf{B}}_1(t)$, we obtain an analytical expression for ${\mathbf{v}}_{\text{trans}}$ as a function of the system's linear response. The linear response and consequently ${\mathbf{v}}_{\text{trans}}$ are influenced by the skyrmion's internal modes and scattering states, as well as by the ferromagnetic background's Kittel mode. The direction and speed of ${\mathbf{v}}_{\text{trans}}$ can be controlled by changing the polarisation, frequency and phase of the driving field ${\mathbf{B}}_1(t)$. For systems with small Gilbert damping parameter $\alpha$, we identify two distinct physical mechanisms used by the skyrmion to move. At low driving frequencies, the skyrmion's motion is driven by friction, and $v_{\text{trans}}\sim \alpha$, whereas at higher frequencies above the ferromagnetic gap, the skyrmion moves by magnon emission, and $v_{\text{trans}}$ becomes independent of $\alpha$.

16 pages (including references), 5 figures. Supplementary: 8 pages. v2: small typos corrected, two references added. v3: minor revisions to the text in response to referee reports, six references added. v4: typos fixed, DOIs added to references. v5: fixed some sign mistakes and added some commas to improve readability of the text

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• Magnon-skyrmion scattering in chiral magnets
• Rotating skyrmion lattices by spin torques and field or temperature gradients
• Inertia and chiral edge modes of a skyrmion magnetic bubble
• Inertia, diffusion and dynamics of a driven skyrmion
• Laser-controlled real- and reciprocal-space topology in multiferroic insulators
• Imaging the ultrafast coherent control of a skyrmion crystal
• Creation of nanometric magnetic skyrmions by global application of circularly polarized microwave magnetic field

Cited by in corpus (5)

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• Emergent electric field from magnetic resonances in a one-dimensional chiral magnet
• Soliton penetration from edges in a monoaxial chiral magnet